Lumen supports a technology called oEmbed, which is how you should embed YouTube and Slideshares (among other things) in open courses. You can also use iframes, though those are a second-best option.

YouTube

To embed a YouTube video, go to video’s YouTube page. Look for the “Share” button under the video, and copy the URL in the Share bar. This address will typically start with “https://youtu.be”. Paste this into your Lumen text.

The code will look like this:

https://youtu.be/fy65_nWp7NM

and the end result will look like this:

Note: If a YouTube user has prevented the embedding of a video on a web page, the video frame will not appear in your Lumen text. Instead, only the link will be visible. Here’s where you can check if a user has prevented embedding of his/her video content:

Slideshare

To embed an Slideshare presentations, go to the presentation’s page. Copy the URL of the presentation you want to embed from the top of the browser window, and paste it into your Lumen text.

The code will look like this:

http://www.slideshare.net/opencontent/wiley-tedxsandy-33976440

and the end result will look like this: